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Blood Gas Analysis – Procedure, Values & Significance

Blood gas analysis (BGA) is a diagnostic test that measures oxygen and carbon dioxide levels as well as the acid-base balance in the blood.

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Things worth knowing about "Blood Gas Analysis"

Blood gas analysis (BGA) is a diagnostic test that measures oxygen and carbon dioxide levels as well as the acid-base balance in the blood.

What is Blood Gas Analysis?

Blood gas analysis (BGA), also known as an arterial blood gas (ABG) test, is a laboratory procedure that measures the levels of oxygen (O₂) and carbon dioxide (CO₂) in the blood, along with the pH value and other parameters of the acid-base balance. Results are available within minutes, making this test an essential tool in emergency and intensive care medicine.

How is Blood Gas Analysis Performed?

A small sample of blood is collected and analyzed. Depending on the clinical question, two main methods are used:

Arterial blood gas analysis (ABG): Blood is drawn from an artery, most commonly the radial artery at the wrist. This is considered the gold standard and provides the most accurate assessment of lung function and gas exchange.
Capillary blood gas analysis: Blood is obtained from a capillary vessel, for example by a fingertip or earlobe prick. This method is less invasive and is frequently used in children.

The collected blood sample is then inserted directly into a specialized analyzer, which automatically measures all relevant parameters.

Which Parameters are Measured?

Blood gas analysis provides a range of important values:

pH value: Indicates the acidity of the blood. Normal range: 7.35–7.45.
pO₂ (partial pressure of oxygen): Measures dissolved oxygen in the blood. Normal arterial range: 70–100 mmHg.
pCO₂ (partial pressure of carbon dioxide): Measures dissolved CO₂. Normal arterial range: 35–45 mmHg.
HCO₃⁻ (bicarbonate): A key blood buffer, reflecting metabolic changes. Normal range: 22–26 mmol/L.
Base Excess (BE): Indicates whether there is an excess or deficit of buffer bases. Normal range: −2 to +2 mmol/L.
Oxygen saturation (SpO₂/SaO₂): The percentage of hemoglobin carrying oxygen. Normal range: 95–99%.

When is Blood Gas Analysis Used?

Blood gas analysis is performed in a wide range of clinical situations, including:

Assessment of respiratory disorders such as asthma, COPD, or pneumonia
Monitoring patients on mechanical ventilation
Diagnosis and follow-up of acid-base disorders (acidosis, alkalosis)
Emergency diagnostics in cases of unconsciousness, shock, or poisoning
Post-operative monitoring after surgical procedures
Evaluation of kidney function in relation to acid-base balance

Interpretation of Results

Interpreting blood gas results requires medical expertise. The following main disorders are distinguished:

Respiratory acidosis: Low pH, elevated pCO₂ – indicates hypoventilation (insufficient breathing).
Respiratory alkalosis: High pH, low pCO₂ – indicates hyperventilation (excessively rapid breathing).
Metabolic acidosis: Low pH, low HCO₃⁻ – may indicate renal failure, diabetic ketoacidosis, or severe fluid loss.
Metabolic alkalosis: High pH, high HCO₃⁻ – may result from severe vomiting or excessive antacid use.

Risks and Side Effects

Blood gas analysis is a safe procedure. With arterial sampling, occasional complications may include:

Brief pain or burning at the puncture site
Bruising (hematoma)
In very rare cases: vascular injury or local infection

Capillary sampling carries even fewer risks and is generally associated with only minimal discomfort.

References

Larsen R. - Anaesthesia and Intensive Care Medicine. Springer, 9th edition, 2016.
German Society for Pneumology and Ventilatory Medicine (DGP) - Guidelines on Blood Gas Analysis and Acid-Base Balance. AWMF, 2019.
Kellum JA et al. - Disorders of Acid-Base Balance. Critical Care Medicine, 2021. PubMed PMID: 33974856.

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